The present invention relates to a method of coalescing and separating oil from a dispersion of oil in water.
The standards are rapidly increasing for the purity level of contaminated water released from a ship or barge into port areas and other bodies of water. There is a particular problem in purifying large quantities of bilge water containing significant quantities of oil. At the present time, one standard commonly used in the United States is that the purity is unacceptable if a visible plume of oil is detected in discharged bilge water. This corresponds to an oil content in the water of on the order of 10 parts per million (ppm).
A particular problem is presented in the discharge of ballast from ships and barges in that in many port areas a ship cannot be safely maneuvered into docking if the ballast is discharged out of port. Accordingly, it is necessary for the discharge to occur in port. Because conventional systems have not been developed for removing sufficient quantities of oil from the ballast water on board the ships (e.g., tankers) or barges, service companies have been developed which will receive pumped ballast water and remove the oil in permanent land-based installations of high capital outlay. This is relatively expensive to the ship or barge owners.
To date, no satisfactory system has been developed for purifying ballast and other bilge water capable of use directly on board ship or in an inexpensive floating system to meet the stringent discharge standards of the United States ports.
A number of systems have been employed for the removal of oil from a dispersion of oil in water. One such system employs granules of plastic materials such as polyethylene and polytetrachloroethylene as a bed through which the dispersion is passed. The oil droplets tend to coat the resin particles and it is necessary to periodically regenerate the resin particles as by shutting down the system and passing a solvent for the oil through the particles. This is quite costly and time consuming. In addition, no known system utilizing such resin particles has been known to produce the types of purities required for the discharge of bilge water at ports of high effluent standards. Furthermore, it is not believed that any such systems have been adapted to shipboard use to accomodate the pitching and rolling of even moderate seas.